The paper presents a cost effectiveness assessment of the safety in a design code for oil tankers. The marginal cost to safety improvements is based on code calibration studies for different target reliabilities. This allows basing the actual target reliability indices on risk acceptance criteria derived from cost effectiveness of the marginal change in scantling requirements. This approach is in agreement with the criteria defined in IMO submissions and used in the ongoing IMO coordinated Formal Safety Assessment studies on bulk carriers. The documentation that cost effectiveness criteria may be applied has previously been submitted to IMO. It is concluded that the method works quite well in the examples that are presented, and that the current codes are in close agreement with decision criteria used for other risk control options. As probabilities calculated by structural reliability methods are notional, it is also advantageous to use marginal costs to safety improvement instead of absolute numbers of probabilities as acceptance criterion. It is indicated that a cost effectiveness criterion may replace the current practice of basing target reliabilities on calibration against previous best practices. Although the basic safety philosophy is changed radically, the study does not indicate that the change in criteria would result in much change in design. The advantage of using the suggested approach is the consistency with ongoing FSA development at IMO.

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